This invention relates to a regulating drawing unit forming part of a sliver drawing frame. The unit includes an inlet measuring organ for a plurality of slivers entering the unit, at least one drawing field, a drive system and a control (regulation) for the drive system. The control responds to a measuring signal emitted by the inlet measuring organ in order to alter the draft by the drive system in the drawing field in such a manner that fluctuations in the input sliver mass are corrected.
Published European Patent Application 477 589 discloses a regulating drawing unit in two embodiments for regulating the slivers. According to the first embodiment, two measuring organs are provided for the throughgoing fiber material: one measuring organ is situated at the inlet and the other is disposed at the outlet of the drawing unit. At the inlet of the drawing unit the entire cross section of the inputted slivers is measured by a measuring condenser constituting the inlet measuring organ. The fluctuating fiber mass of the slivers which runs between the condenser plates with a speed of approximately 150 m/min acts as the dielectric of the condenser. Due to the difficulties experienced at the inlet side measuring, the regulation is so designed that the measuring errors are compensated for by means of an adaptive regulation. For this purpose at the outlet of the drawing unit a further measuring organ (outlet measuring organ) is provided. Problems and errors involved in measurement techniques are considered in the known regulating system by virtue of the fact that the measuring signals of the outlet measuring organ are taken into account to adapt the regulation to the inlet-side measuring errors. It is therefore a necessary requirement that a measuring organ be disposed before and after the regulating path, that is, in a principal drawing region. Such an arrangement is structurally complex. Further, the running time of the fiber material between the measuring locations at the inlet and at the outlet have to be taken into consideration. It is a further disadvantage that the running speed of the individual slivers through the outlet measuring organ are approximately six times higher than the running speed of the slivers through the inlet measuring organ. Taking into account these effects at high speeds and short reaction times requires a very complex regulating system.
According to the second embodiment disclosed in the European application 477 589 only an outlet measuring organ is provided whose structure is different from the inlet measuring organ of the first embodiment and responds directly to the fiber mass (that is, to the cross section of the sliver). The outgoing sliver is compressed with a sensor roll pair formed of a grooved roller and a tongue roller and thereafter the thickness of the compressed fiber material is evaluated as a measure for the outgoing fiber mass. The disadvantage of such a measuring procedure resides in that the compression (densification) of the fiber material is, among others, dependent from its throughgoing speed, that is, the measuring signal is speed-dependent. Such a speed dependency means that the same sliver quantity (for example, a length of 15 m) yields different thickness measurements for different sliver speeds. Such a disadvantage is experienced during the acceleration and deceleration of the machine, that is, during velocity variations. In high-performance drawing frames of current design (which operate with sliver speeds of 1,000 m/min and above) a coiler can is, at the outlet of the drawing frame, filled in about 5 to 7 minutes, and for replacing the coiler can, the operating speed is reduced to a very low speed or even to a standstill. During the accelerating and decelerating steps the measured density values of approximately 10 to 15 m length of sliver introduced into the coiler can have been affected in an undesired manner because of the speed dependency. Such occurrence also adversely affects the equalization of the mass fluctuations of the slivers in the drawing unit. It is a disadvantage, among others, that the measurement is effected during the high delivery speed of the individual outgoing slivers which is approximately six times higher than the speed of the slivers introduced into the drawing unit. It is an even more serious drawback that with the outlet measuring organ no automatic optimization by subsequent verification of the results is possible because the outlet measuring organ constitutes the last monitoring point for the obtained results.